TEK2225 not focusing

[dutchbird]

Hello everybody,

I have a tek2225 scope and today I can not get the trace on the screen focused anymore 😕. It appears that the pot has not enough range. Fully CCW is the best position, but still not focused.

I saw some post about adding (and changing) resistors around the pots HV part. Can anyone help me to get this problem tackled. For instance with the schematic of this part.

Thanks in advance,
Dutchbird

 

[Gyuri]

There are two good videos:
Tektronix 2225 Oscilloscope Teardown and Calibration - EEVblog #208 - YouTube
Tektronix 2225 Analog Oscilloscope - EEVblog #196 - YouTube

 

[Gyuri]

Here is a Tektronix 2225 service manual:
https://skydrive.live.com/?cid=e894cb7d50b65fbf#cid=E894CB7D50B65FBF&id=E894CB7D50B65FBF%21646

 

[dutchbird]

Here is a Tektronix 2225 service manual:
https://skydrive.live.com/?cid=e894cb7d50b65fbf#cid=E894CB7D50B65FBF&id=E894CB7D50B65FBF!646

Gyuri, this helps a lot! Thank you!

 

[dutchbird]

Gyuri, I have fixed the problem the scope is now well focused.
Resistor R984 was increased to ~2M, instead of 1M, as mentioned in the schematic ... I have replaced the part.

Thanks again for your help!
Dutchbird